Carats are the best known measure associated with diamonds. That said, many people probably don’t know what the word means. And if you ask them what, say, a 3-carat diamond looks like, they will probably be at a loss.

Carats are used to measure a diamond’s weight. One carat equals 0.2 grams. Why this specific unit of measurement, though? The practice dates back to the Middle Ages, when the weight of gems was measured against carob (Ceratonia siliqua) seeds, known for almost always having the same weight: 0.2 grams. That is where the word «carat» comes from.

Diamonds of the same diameter may differ in weight. The round cut, which is considered a classic, is usually provided as reference in special tables. Experts use a special ruler to measure the gem’s dimensions, and consult the table to determine its carat weight. For example, the diameter of a 1-carat round diamond would be 6.4 mm.

Documents that are attached to diamond jewelry usually list the carat weight to three decimal places. That is, if a diamond weighs 3 carats, its weight will be written down as 3.000.